U.S. patent application number 11/042411 was filed with the patent office on 2006-05-25 for method and system for selecting transmit antennas to reduce antenna correlation.
This patent application is currently assigned to InterDigital Technology Corporation. Invention is credited to Jung-Lin Pan, Yingming Tsai.
Application Number | 20060111054 11/042411 |
Document ID | / |
Family ID | 36461545 |
Filed Date | 2006-05-25 |
United States Patent
Application |
20060111054 |
Kind Code |
A1 |
Pan; Jung-Lin ; et
al. |
May 25, 2006 |
Method and system for selecting transmit antennas to reduce antenna
correlation
Abstract
A method and system is disclosed for transmitting data over at
least one transmit antenna to reduce antenna correlation in
wireless communication systems. The transmit antennas are comprised
of randomly selected antenna elements wherein the antenna elements
are randomly selected from antenna elements of a plurality of
antennas of a node in a wireless communication system. The number
of antenna elements in a group of randomly selected antenna
elements may be fixed or may vary over time.
Inventors: |
Pan; Jung-Lin; (Selden,
NY) ; Tsai; Yingming; (Boonton, NJ) |
Correspondence
Address: |
VOLPE AND KOENIG, P.C.;DEPT. ICC
UNITED PLAZA, SUITE 1600
30 SOUTH 17TH STREET
PHILADELPHIA
PA
19103
US
|
Assignee: |
InterDigital Technology
Corporation
Wilmington
DE
|
Family ID: |
36461545 |
Appl. No.: |
11/042411 |
Filed: |
January 25, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60629963 |
Nov 22, 2004 |
|
|
|
Current U.S.
Class: |
455/101 ;
455/97 |
Current CPC
Class: |
H04B 7/0691 20130101;
H04B 7/0606 20130101 |
Class at
Publication: |
455/101 ;
455/097 |
International
Class: |
H04B 7/02 20060101
H04B007/02 |
Claims
1. In a wireless communication system, a method of selecting
antennas to transmit data, the method comprising: establishing an
antenna size for a virtual transmit antenna wherein antenna size is
defined as a number of antenna elements making up the virtual
transmit antenna; and selecting antenna elements from an antenna
array to create the virtual transmit antenna wherein the number of
antenna elements selected is equal to the antenna size of the
virtual transmit antenna and less than an array antenna size of the
antenna array.
2. The method of claim 1 comprising providing the antenna size as a
fixed size.
3. The method of claim 2 comprising: changing the selected antenna
elements making up the virtual transmit antenna by re-establishing
antennas from which the antenna elements were selected; and
performing an antenna hopping sequence, the antenna hopping
sequence extending across the antenna array.
4. The method of claim 3 wherein said antenna hopping sequence
provides antenna diversity in an azimuth direction while
maintaining a substantially constant elevation direction.
5. The method of claim 3 wherein said antenna hopping sequence
provides antenna diversity in both azimuth and elevation
directions.
6. The method of claim 1 further comprising establishing antennas
from an antenna array including establishing antenna size, such
that a configuration of the antennas established from an antenna
array establishes the antenna size.
7. The method of claim 6 comprising: changing the antenna
configuration by re-establishing the antennas; and performing an
antenna hopping sequence, the antenna hopping sequence extending
across plural antenna configurations of the same antenna array.
8. The method of claim 7 comprising maintaining a substantially
constant antenna size across plural antenna hops in the antenna
hopping sequence.
9. The method of claim 6 wherein said antenna hopping sequence
provides antenna diversity in an azimuth direction while
maintaining a substantially constant elevation direction.
10. The method of claim 6 wherein said antenna hopping sequence
provides antenna diversity in both azimuth and elevation
directions.
11. A multiple in/multiple out (MIMO) wireless communication system
comprising: a circuit configured to establish an antenna size for a
virtual transmit antenna wherein antenna size is defined as a
number of antenna elements making up the virtual transmit antenna;
and a circuit configured to randomly select antenna elements from
an antenna array to create the virtual transmit antenna wherein the
number of antenna elements selected is equal to the antenna size of
the virtual transmit antenna and less than an array antenna size of
the antenna array.
12. The MIMO communication system of claim 11 wherein the circuit
configured to randomly select antenna elements is further
configured to provide a fixed antenna size.
13. The MIMO communication system of claim 12 comprising: the
circuit configured to randomly select antenna elements making up
the virtual transmit antenna by re-establishing antennas from which
the antenna elements were selected; and a circuit configured to
perform an antenna hopping sequence, the antenna hopping sequence
extending across the antenna elements.
14. The MIMO communication system of claim 13 wherein said circuit
for performing an antenna hopping sequence provides antenna
diversity in an azimuth direction while maintaining a substantially
constant elevation direction.
15. The MIMO communication system of claim 13 wherein said circuit
for performing an antenna hopping sequence provides antenna
diversity in both azimuth and elevation directions.
16. The MIMO communication system of claim 11 wherein the circuit
configured to randomly selected antenna elements is further
configured to establish antennas from an antenna array including
establishing antenna size, such that a configuration of the
antennas established from an antenna array establishes the antenna
size.
17. The MIMO communication system of claim 16 comprising: the
circuit configured to randomly select antenna elements being
further configured to change the antenna configuration by
re-establishing the antennas; and a circuit for performing an
antenna hopping sequence, the antenna hopping sequence extending
across plural antenna configurations of the same antenna array.
18. The MIMO communication system of claim 17 wherein said circuit
for performing an antenna hopping sequence provides antenna
diversity in an azimuth direction while maintaining a substantially
constant elevation direction.
19. The MIMO communication system of claim 17 wherein said circuit
for performing an antenna hopping sequence provides antenna
diversity in both azimuth and elevation directions.
20. The MIMO communication system of claim 17 wherein the circuit
for randomly selecting antenna elements maintains a substantially
constant antenna size across plural antenna hops in the antenna
hopping sequence.
21. An integrated circuit device comprising: a circuit configured
to establish an antenna size for a virtual transmit antenna wherein
antenna size is defined as a number of antenna elements making up
the virtual transmit antenna; and a circuit configured to randomly
select antenna elements from an antenna array to create the virtual
transmit antenna wherein the number of antenna elements selected is
equal to the antenna size of the virtual transmit antenna and less
than an array antenna size of the antenna array.
22. The integrated circuit device of claim 21 further comprising: a
circuit configured to receive and process feedback information
provided from a receiver site; and a circuit configured to select
virtual transmit antennas for which satisfactory feedback
information has been received to transmit data to the receiver
site.
23. The integrated circuit device of claim 22 wherein the feedback
information comprises an antenna identification number.
Description
CROSS REFERENCE TO RELATED APPLICATION(S)
[0001] This application claims the benefit of U.S. Patent
Application No. 60/629,963, filed Nov. 22, 2004 which is
incorporated by reference as if fully set forth.
FIELD OF INVENTION
[0002] The present invention is related to wireless communication
systems. More particularly, the present invention is related to a
method and system for selecting transmit antennas to reduce antenna
correlation.
BACKGROUND
[0003] Multiple-input multiple-output (MIMO) refers to a type of
wireless transmission and reception scheme where both the
transmitter and receiver employ more than one antenna. Special
cases of MIMO are when there is a single antenna on the receiver
side and multiple antennas on the transmit side, called
single-input multiple-output (SIMO), and when there are multiple
antennas on the receiver side and one antenna on the transmitter
side, called multiple-input single-output (MISO), and a traditional
transmission scheme with one antenna on both sides is a
Single-Input Single-Output (SISO).
[0004] A MIMO system takes advantage of the spatial diversity or
spatial multiplexing options created by the presence of multiple
antennas and improves signal to noise ratio and increases
throughput. It has been seen in the past that multipath (once a big
hurdle in wireless communications) can help improve the overall
performance if it is processed properly by the transmitter and the
receiver. Essentially, each multipath component carries information
about the transmitted signal, therefore if the multipath components
are resolved and collected appropriately they should reveal more
information about the transmitted signal.
[0005] An antenna correlation is one of the factors causing
diversity reduction and capacity decrease of multiple antenna
systems, such as multiple-input/multiple-output (MIMO) systems, in
wireless communication. Antenna correlation is a correlation
measurement between the different signal propagation paths of the
transmit and receive antennas. For an antenna system having N
transmit antennas and M receiving antennas, a correlation matrix of
dimension M by N is usually used to describe the antenna
correlation between transmit and receive antennas.
[0006] A conventional MIMO system selects particular transmit
antennas for transmission which enhances performance. The
conventional MIMO system requires antenna feedback information to
perform the selection of transmit antennas. The most common
feedback information is the channel impulse response. Usually the
feedback information comes from the receiver wherein the receiver
estimates the channel impulse responses and sends them back to the
transmitter for processing. The process for obtaining the feedback
information is usually complex and is not easy to implement.
[0007] Therefore, it would be desirable to provide a method and
system wherein antenna selection may be accomplished with little or
no feedback information provided to a transmitter.
SUMMARY
[0008] The present invention is a method and system for
transmitting data over at least one transmit antenna to reduce
antenna correlation in wireless communication systems. The transmit
antennas are comprised of randomly selected antenna elements
wherein the antenna elements are randomly selected from antenna
elements of a plurality of antennas of a node in a wireless
communication system. The number of antenna elements in a group of
randomly selected antenna elements may be fixed or may vary over
time.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 shows a system for implementing transmit antenna
selection to reduce antenna correlation in accordance with the
present invention.
[0010] FIG. 2 is a block diagram of a transmitter configured to
perform transmit antenna selection in accordance with the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0011] The present invention provides a transmit antenna selection
(i.e. antenna hopping) technique that effectively reduces antenna
correlations at a transmit antenna and a receive antenna, thereby
providing increased diversity and enhanced capacity in a wireless
communication system. The antenna hopping technique of the present
invention does not require any feedback information. Therefore, a
system in accordance with the present invention is less
complicated, easy to implement, and increases system capacity by
reducing antenna correlation.
[0012] The present invention is applicable to any type of wireless
communication system including, but not limited to, cellular
systems, mobile systems, wireless LANS, MANS, and PANS, fixed
access systems, and ad-hoc/mesh networks. Examples of such wireless
communication systems include 1G through 3G cellular systems (AMPS,
IS-136, GSM/GPRS/EDGE, IS-95, CDMA2000, UMTS FDD/TDD) and the
802.xx family (802.11, 802.16, 802.15).
[0013] Herein, a wireless transmit/receive unit (WTRU) includes but
is not limited to a user equipment, mobile station, fixed or mobile
subscriber unit, pager, or any other type of device capable of
operating in a wireless environment. When referred to herein, a
base station includes but is not limited to a Node-B, site
controller, access point (AP) or any other type of interfacing
device in a wireless environment. For convenience in describing the
present invention, a base station is a "transmitting terminal,"
however, any node capable of transmitting communication signals may
be the transmitting terminal. Similarly, for convenience in
describing the present invention, a WTRU is a "receiving terminal,"
however any node capable of receiving communication signals may be
the receiving terminal.
[0014] FIG. 1 is a diagram of a wireless communication system 100
in accordance with the present invention. The system 100 includes a
plurality of antennas 102, 104, 106, 108 that make up an antenna
array of a single wireless entity which, in this case, is a base
station (not shown). Each antenna 102, 104, 106, 108 includes a
plurality of antenna elements 110. In a preferred embodiment of the
present invention, various antenna elements 110 from each antenna
102, 104, 106, 108 may be grouped virtually where each virtual
grouping of antenna elements effectively function as a single
transmit antenna (i.e. a virtual transmit antenna having elements
spanning any number of physical antennas). By way of example, in
FIG. 1, three transmit antennas are shown 112, 114, 116.
[0015] The antenna elements 110 are preferably selected "randomly"
according to a pseudo-random number generator or based on some
predetermined randomized random, pseudorandom or other non-random
predetermined pattern sequence. While a true random selection is
possible, the random selection according to the present invention
can be effected with pseudo-random selection. This produces a
random effect as used in the invention. As used herein, "random"
and "random selection" includes pseudo-random and pseudo-random
selection.
[0016] Each time a randomized set of antenna elements are selected,
data is transmitted over that particular randomized set of antenna
elements, wherein the randomized set of antenna elements
effectively operate as a single transmit antenna. This results in
the data being transmitted in a similar randomized fashion over the
entire set of antenna elements according to the randomized
selection, which is considered to be a form of antenna hopping.
Data transmissions follow the antenna hopping patterns. Random
selection has the advantage of not requiring feedback information
from a receiver and simplifies the systems as compared to
pre-selection methods.
[0017] At any given point in time, each group of antenna elements
110 will have a particular degree of correlation. Thus, one group
of antenna elements 110 may experience high correlation, for
example transmit antenna 114, while certain combinations of
antennas do not, for example transmit antennas 112 and 116.
Ideally, one would use the transmit antennas 112, 116 having low
correlation for data transmission at any given time. It has been
found, however, that such arrangements are often difficult or
expensive to implement and sometimes are not even feasible.
Therefore, pursuant to a preferred embodiment of the present
invention, random selection of antennas or antenna hopping can
achieve a similar goal, but with reduced complexity.
[0018] For example, in the present invention, even though at any
time a "bad" combination of antenna elements (i.e. a combination of
antenna elements having high correlation) may occur, because of
randomness, the frequency of such "bad" combination is at a low
level. Therefore, despite the possibility of a "bad" combination,
in the long run, the overall performance of the antenna system is
enhanced and antenna diversity is increased with reduced system
complexity.
[0019] It is noted that antenna hopping in accordance with the
present invention can artificially create fast fading conditions
from slow fading. This is beneficial, for example, when wireless
users are in deep and slow fading for certain antenna transmission
and reception. By using antenna hopping, the deep and slow fading
conditions can be alleviated and burst error can be avoided. The
antenna diversity can be achieved in both azimuth and elevation
directions. In fast fading the "bad" signal can become a "good"
signal in a short period of time, while in slow fading the "bad"
signal will remain "bad" for a long period of time before it
becomes a "good" signal. By randomly hopping the signal around
transmit antennas, it creates the fast fading scenario.
[0020] It should be clear that it is possible to provide
configurations in which each transmit antenna 112, 114, 116 is
substantially identical in size or other aspects of configuration.
It is also possible to perform other configuration changes such as
arranging dipoles in opposite polarities or arranging elements
singularly or in pairs of elements which are not in alignment.
[0021] In each arrangement, the size of a transmit antenna is
defined in the context of the present invention as the number of
antenna elements making up a particular transmit antenna. In
accordance with a first embodiment of the invention, the size of
antennas is selected randomly each time, and then the antennas are
randomly selected according to the selected size. Antenna size can
be pre-configured or dynamically configured during the run time.
Likewise, the antenna configuration can be dynamically changed or
pre-configured. For example, the antenna size is selected randomly
each time the system decides to change antenna size to optimize
performance or for other reasons.
[0022] This approach uses a dynamically configurable method which
can allow the antenna size to be changed during the run time. For
example, M1 antenna elements are selected from among 1, 2, . . . ,
M.sub.T antenna elements. In this case, there are
C.sub.M.sub.1.sup.M.sup.T possible combinations for selecting M1
antenna elements from M.sub.T antenna elements. Next time the
antenna size is adjusted, the antenna size is again selected
randomly from 1, 2, . . . , M.sub.T, say M2, and then, M2 antennas
are selected randomly from among M.sub.T antennas. In this case,
there are C.sub.M.sub.2.sup.M.sup.T possible combinations.
[0023] In accordance with a second embodiment, the size of antennas
is fixed and the antennas are randomly selected according to the
fixed size. For example, assume antenna size is fixed and
predetermined at say, M. In this case, M antenna elements are
selected randomly among M.sub.T antenna elements each time the
system decides to change antenna size to optimize performance or
for other reasons. The selected antennas belong to one of the
C.sub.M.sup.M.sup.T possible combinations.
[0024] By determining the size of the transmit antennas as
explained above, the correlation between antennas is reduced
because the signal hops around the selected antenna elements based
on the pre-determined antenna size thereby avoiding the bad antenna
combinations (i.e. those with high antenna correlation) over time.
It is noted that the antenna hopping technique in accordance with
the present invention is applicable to both 2-D wireless systems
with azimuth as a parameter and 3-D wireless systems with both
azimuth and elevation as parameters. For 2-D wireless systems, the
correlation reduction occurs in azimuth. For 3-D wireless systems,
the reduction in correlation may occur in both azimuth and
elevation.
[0025] Referring now to FIG. 2, there is shown an antenna hopping
transmitter 200. The antenna hopping transmitter 200 includes a
transmitter 202, a switching device 204, an antenna hopping
controller 206, and a plurality of antennas 208. As explained
above, each antenna 208 includes a plurality of antenna elements
(not shown). The transmitter 202 outputs a data signal to the
switching device 204. The switching device 204 transmits the signal
over a randomly selected group of antenna elements to increase the
diversity with which the signal is being transmitted. The antenna
elements are randomly selected from the antenna elements of the
antennas 208 according to a random selection generated by the
antenna hopping controller 206. The randomly selected antenna
elements preferably vary over time. Further, the number of elements
selected as part of a randomly selected group of antenna elements
may be fixed or may be dynamically adjusted according to a
particular algorithm.
[0026] Although feed-back information is not required when
implementing the teachings of the present invention, it may be
utilized in alternate embodiments. Therefore, in a preferred
embodiment, signals received at a receiver are processed by the
receiver to determine signal quality, antenna correlations, and
other related measurements for each transmit antenna at the
transmitter. Preferably, identification numbers are sent back
identifying the transmit antennas from which signals are being
received with satisfactory measurements. The feedback of antenna
identification numbers simplifies the system and results in less
data being sent back to the transmitter for processing. For
example, in the present invention, transmit antenna identification
numbers may be 1, 2, 3, . . . N depending on the number of active
transmit antennas (i.e. those actually transmitting data) and the
maximum number of antennas at the transmit site, say N. For a
transmit site having eight antennas, the feedback information
consists of only three binary numbers. This is much less
complicated than processing of channel impulse responses as in
currently known systems. In currently known systems, assuming there
are L paths for channel impulse response per antenna, feedback
information may require L complex numbers for each antenna. For
example, there will be N times L complex numbers to be feedback to
the transmitter and each complex number requires two floating
numbers wherein each floating number may require some amount of
binary numbers, say Q, to be represented. This arrangement results
in significantly more processing being performed at the transmit
site in order to process the feedback information.
[0027] It is noted that additional information may be provided
along with the identification numbers. For example, information
such as channel state, antenna correlation, signal quality, etc.
may be feedback along with the identification numbers.
[0028] Although the elements in the Figures are illustrated as
separate elements, these elements may be implemented on a single
integrated circuit (IC), such as an application specific integrated
circuit (ASIC), multiple ICs, discrete components, or a combination
of discrete components and IC(s).
[0029] Although the features and elements of the present invention
are described in the preferred embodiments in particular
combinations, each feature or element can be used alone without the
other features and elements of the preferred embodiments or in
various combinations with or without other features and elements of
the present invention. Furthermore, the present invention may be
implemented in any type of wireless communication system.
* * * * *